1. Field of the Invention
The present invention relates to an exhaust gas sensor or analyzer for detecting contaminants in exhaust gas, such as hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NO.sub.x) and the like. The present invention further relates to a method of producing such an exhaust gas sensor. Still further, the present invention relates to a sensor system using such an exhaust gas sensor.
2. Description of the Related Art
It is known to use a resistive type sensor as an analyzer or sensor for detecting the above described contaminants in exhaust gas. In such a sensor, an oxide semiconductor such as a semiconductor made of SnO.sub.2 or the like is used as a detection element for detecting the content of contaminants in exhaust gas depending upon a variation in resistance of the oxide semiconductor in proportion to its absorption of contaminants.
The resistive type sensor has such a characteristic that the output of the detection element made of oxide semiconductor varies depending upon a variation of the concentration of oxygen in the exhaust gas. Due to this, there is caused a problem in that the output for detection of the same concentration of contaminants varies depending upon a variation of the concentration of oxygen in the exhaust gas. Thus, as disclosed in Japanese patent provisional publication No. 5-180794, it has been proposed to send oxygen into the exhaust gas by means of a pump cell made of solid electrolyte and make higher the concentration of oxygen therein for thereby making smaller the relative variation in the concentration of oxygen in the exhaust gas and making higher the detection accuracy. However, there still exists a problem in that if the concentration of oxygen in the exhaust gas varies largely, a sufficient restraining effect on restraint of the relative variation in the concentration of oxygen by the effect of introduction of oxygen from the pump cell cannot be obtained and therefore satisfactory detection accuracy cannot be obtained.